1. Field of the Invention
The present invention relates to a radio communication system having a plurality of base stations each located in each communication area, and more particularly a radio communication system communicating between the base stations having adjacent areas, using frequencies which are not mutually overlapped.
2. Description of the Related Art
As a measure for avoiding a communication failure due to a trouble in a base station constituting the radio communication system, for example, there has been adopted a redundant configuration, such as a duplicated structure, in the equipment configuration of each base station.
When the equipment has duplicated structure, it is necessary to prepare the equipment with hardware and software which realize an identical function in a duplicated manner. This produces an increase of an equipment scale with a complicated equipment configuration, such that processing to share data on the active side and the standby side becomes necessary.
Meanwhile, even when the equipment in the base station is configured of duplicated structure, unless a power unit to supply power to the base station is not duplicated, or a preferential communication path to an upper-level unit is not duplicated, the communication function of the base station itself goes down in the event of a failure in the above units, and communication in the base station communication area becomes impossible. Therefore, in consideration of the occurrence of failure in the communication function of a certain base station, it is necessary to secure a substitutional communication function.
In the cited Patent document 1, there is proposed a method of transferring a stored voice data to the opposite party via a data relay unit in place of a base station, on detecting abnormal speech communication in a mobile telephone network.
[Patent document 1] the official gazette of the Japanese Unexamined Patent Publication No. 2005-294972.
However, according to the method proposed in the cited patent document 1, when the speech communication is abnormally terminated, a message recorded thereafter is transmitted to the opposite communication terminal by use of a communication network different from the mobile telephone network. It is not possible to prevent the disconnection of the communication itself.
In order to prevent communication disconnection even when a communication failure occurs in the base station, it is considered to introduce a redundant configuration to the entire functions necessary for securing communication, such as in the power unit and the communication path to/from the upper-level equipment, in addition to the duplication of the equipment configuration in the base station. However, the above method is not realistic because of requiring a large cost to implement such the system.